1. Field of the Invention
The present invention generally relates to a method of accomplishing bonding without using any bonding agent and, more particularly, to the method of bonding a first member, made of a plastic material, with a second member which may be made of glass, ceramics, metallic material including alloys, plastic material, wood or the like.
2. Description of the Prior Art
Bonding of a plastic member with other member of any material has hitherto and is currently required the use of a bonding agent. The bonding agent for this purpose is nowadays available in various types: room temperature curing type such as, for example, solvent dry bonding agent, catalyst added bonding agent, wet hardening adhesive, anaerobic adhesive, and instant adhesive, thermosetting adhesive, ultraviolet cure adhesive, hot-melt adhesive, remoistening adhesive and pressure sensitive adhesive and so on. Depending on the affinity between members to be bonded together and/or the purpose of bonding, the specific bonding agent is generally utilized to achieve an intended bond.
However, depending on the member to be bonded with a plastic member and/or the application of molded articles, the need is generally recognized to avoid the use of any bonding agent in accomplishing a bonding between the plastic member and the second member of any material in order to pursue the intended chemical resistance, heat resistance, dimensional stability, electric characteristic and/or optical characteristic.
The Japanese Laid-open Patent Publication No. 4-55438, for example, discloses formation of a stack of laminates with or without bonding layers after the bond performance has been increased by irradiating films of poly-parabanic acid. However, where no bonding layer is employed, the technique disclosed therein is applicable only to laminates each having an adhesive property and, therefore, the use of a bonding agent is essential where the laminates having no adhesive property are to be stacked together.
The Japanese Laid-open Patent Publications No. 2001-162645 and No. 2001-162723, for example, discloses a method of bonding a rubber composition and a polyamide material together. According to those patent publications, after the rubber composition has been subjected to the ultraviolet irradiation treatment, the plasma treatment, or the corona discharge treatment, in order for the rubber composition to be bonded with the polyamide material with no bonding agent being used, the polyamide material must be held in a molten state before it is bonded with the rubber composition and, therefore, the technique disclosed therein is incapable of being applied to bonding of materials sensitive to heat.
Discussing by way of a specific material to be bonded, in the planar light source device (for backlighting apparatus such as disclosed in the U.S. Pat. No. 5,396,350) including a light guide element and a microprism arrayed film (optical film), both made of a plastic material, are required to be bonded together to thereby provide integral members for a planar light source device. However, the use of any bonding agent or adhesive film (See the Japanese Laid-open Patent Publications No. 2000-249836 and No. 2001-357709), the integral members for the planar light source device is incapable of being fabricated in a thin-walled structure. Since increase of the thickness of the planar light source device by a quantity corresponding to the thickness of one or more bonding layers results in lowering of the light transmittance and since the manufacturing cost of the planar light source device tends to be incurred as a result of increase of the number of process steps, the need has arisen and is recognized to provide a method of directly bonding the light guide element and the microprism arrayed film together without any bonding agent being used.
The bonding method that does not require the use of any bonding agent is not in non-existence in the art. For example, the Japanese Laid-open Patent Publication No. 2001-356208 discloses a technique of fabricating a film having an array of microprisms with the use of a specific material capable of exhibiting an adhesive property when such material is treated with an ionization radiation. This technique disclosed therein is applicable where the special plastic material is used for the microprism arrayed film and is therefore susceptible to increase in manufacturing cost where no special plastic material is used.